Semiconductor chips can be mounted in a flip-chip configuration, wherein the chips contain solder balls between integrated circuit (IC) devices and chip carriers. The solder balls provide an electrical connection and bond between a chip contact location and a substrate contact location. It is important that the size of the solder balls are uniform in order to ensure that all of the chip contact locations will be electrically interconnected to a corresponding substrate contact location.
Various technologies exist for depositing solder bumps on to IC devices at the wafer level, including, for example, evaporation, electroplating, screen-printing, jetting, ball dropping, and Controlled Collapse Chip Connect New Process (i.e., C4NP). These deposition methods are often referred to as solder wafer bumping or C4 wafer bumping. Originally, solder wafer bumping was accomplished by evaporating both the ball-limiting metallurgy (BLM) and solder through mask holes in an array fashion onto the wafer surface. As the demand for higher I/O density, and lower cost of flip-chip interconnections has increased, however, other deposition methods have been developed. For example, ball drop methods, used to make micro-size solder balls, have recently gained attention in the industry because these methods allow for flexibility in the solder alloys used and finer pitch applications. Indeed, in U.S. Pat. No. 6,517,602, Sato et al. disclose a method of forming solder balls by using a droplet spraying method. This method enables production of micro-sized solder balls, but does not enable formation of solder balls having diameters less than 50 microns due to nozzle-size limitations. Furthermore, the process described by Sato et al. does not produce uniform solder balls, and thus a secondary sorting process is needed to obtain solder balls of the same size.
More recently, injection molded solder (IMS) processing has been used as a cost-effective solder wafer bumping method. While solder balls formed by IMS are usually more uniform in size than those produced by “ball drop” techniques, the uniformity of the solder balls can be lost if the solder balls escape from the mold plate and are allowed to merge with one another after reflowing occurs. Therefore, it would be desirable to develop an IMS process wherein merging or bridging of the solder balls is reduced or prevented.